Stormwater treatment apparatus

ABSTRACT

A liquid purification and separation apparatus for separation of pollutants in stormwater runoff is disclosed. This apparatus utilizes gravitational separation and tortuosity, resulting from a plurality of baffles both perpendicular to and oblique to the primary water flow direction, to trap substances less-dense and more-dense than water. The apparatus features improved resistance to pollutant remobilization through treatment of water volume rather than flow rates, using vertically stacked water columns of varying depths to settle small particles. An overflow structure diverts excessive liquid without interfering with purification and separation, and can be placed integrally within or external to the apparatus receptacle.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/487,097, filed Jan. 19, 2000, now U.S. Pat. No. 6,350,374,entitled “Stormwater Treatment Apparatus” and incorporated in itsentirety herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Apparatus for treatment of stormwater runoff throughvolume-control-based detention and minimization of pollutantremobilization.

2. Description of the Related Art

This invention relates generally to liquid purification and separationand, more specifically, to an apparatus for separation of pollutants inurban stormwater runoff from the runoff water. This apparatus utilizesgravitational separation and tortuosity, resulting from a plurality ofbaffles both perpendicular to and oblique to the primary water flowdirection, to trap substances less-dense and more-dense than water. Thisinvention is differentiated from prior art by improved resistance topollutant remobilization, resulting from an iterative experimentalhydraulic design process. In addition, this invention provides a degreeof retention through volume-control that exceeds that provided byexisting gravitational, sub-surface, stormwater treatment systems.

Impacts of stormwater runoff on receiving environments have beendocumented extensively in engineering and scientific literature. Section402 of the Federal Clean Water Act (CWA) regulates stormwater dischargesthrough the National Pollutant Discharge Elimination System (NPDES).Treatment of stormwater runoff using best management practices (BMPs) isa typical requirement of state and local regulations, as well. In the1990s, there has been growing interest in ‘ultra-urban/space limited’BMP's, such as sand filters, water quality inlets, and, reservoir/vaulttype of structures. Space constraints, high property values, soilconditions, and the proximity of other building foundations oftenpreclude the use of conventional, space-intensive stormwater BMP's suchas detention ponds. For in-fill construction or redevelopment inbuilt-up urban areas, where pollutant loads from urban runoff areusually the greatest, unconventional stormwater treatment technologiesmay be necessary.

Vault-type treatment technologies have been widely used for stormwatertreatment in urban areas; however, the effectiveness of these devicesfor removal of suspended solids and oil and grease has been onlymarginal. A great weakness of these types of devices has been that largestorm events tend to flush out the system, thereby releasing pollutantsthat were previously removed.

Prior art in the field of this invention of which the applicant is awareincludes the following:

U.S. Pat. No. 4,127,488, Bell, J. A. et al., November 1978, Method andapparatus for separating solids from liquids.

U.S. Pat. No. 4,136,010, Pilie, R. J. et al., January 1979, Catch basininterceptor.

U.S. Pat. No. 4,328,101, Broden, C. V., May 1982, Device for separatingparticulate matter from a fluid.

U.S. Pat. No. 4,363,731, Filippi, R., December 1982, Device forregulating the flow of waste waters.

U.S. Pat. No. 4,383,922, Beard, H. J., May 1983, Waste water clarifier.

U.S. Pat. No. 4,983,295, Lamb, T. J. et al., January 1991, Separator.

U.S. Pat. No. 4,985,148, Monteith, J. G., January 1991, Improvedseparator tank construction.

U.S. Pat. No. 5,004,534, Buzzelli, V., April 1991, Catch basin.

U.S. Pat. No. 5,186,821, Murphy, D. T., February 1993, Wastewatertreatment process with cooperating velocity equalization, aeration, anddecanting means.

U.S. Pat. No. 5,342,144, McCarthy, E. J., August 1994, Stormwatercontrol system.

U.S. Pat. No. 5,520,825, Rice, W. M., May 1996, Oil-water separator.

U.S. Pat. No. 5,536,409, Dunkers, K. R., July 1996, Water treatmentsystem.

U.S. Pat. No. 5,637,233, Earrusso, P. J., June 1997, Method andapparatus for separating grease from water.

U.S. Pat. No. 5,679,258, Petersen, R. N., October 1997, Mixed immiscibleliquids collection, separation, and disposal method and system.

U.S. Pat. No. 5,759,415, Adams, T., June 1998, Method and apparatus forseparating floating and non-floating particulate from rainwaterdrainage.

U.S. Pat. No. 5,788,848, Blanche, P. et al., August 1998, Apparatus andmethods for separating solids from flowing liquids or gases.

U.S. Pat. No. RE30,793, Dunkers, K. R., November 1981, Apparatus forwater treatment.

In addition to the patents listed above, a number of inventions in thegeneral field of stormwater treatment methods and devices werediscovered during the patent search. The inventions listed below have anelement or elements similar to the invention disclosed herein; however,additional elements, details of elements, and/or applications of theinventions differ significantly from the forms and functions of thepresent invention. While the inventions listed below are intended toprovide stormwater treatment, the principle of operation for many ofthese devices is filtration rather than sedimentation.

U.S. Pat. No. 4,298,471, Dunkers, K. R., November 1981, Apparatus forequalization of overflow water and urban runoff in receiving bodies ofwater.

U.S. Pat. No. 4,377,477, Dunkers, K. R., March 1983, Apparatus forequalization of overflow water and urban runoff in receiving bodies ofwater.

U.S. Pat. No. 4,664,795, Stegall, W. A. et al., May 1987, Two-stagewaste water treatment system for single family residences and the like.

U.S. Pat. No. 4,747,962, Smissom, B., May 1988, Separation of componentsof a fluid mixture.

U.S. Pat. No. 4,865,751, Smissom, B., September 1989, Separation ofcomponents of a fluid mixture.

U.S. Pat. No. 5,080,137, Adams, T. R., January 1992, Vortex flowregulators for storm sewer catch basins.

U.S. Pat. No. 5,232,587, Hegemier, T. E. et al., August 1993, Stormwaterinlet filters.

U.S. Pat. No. 5,322,629, Stewart, W. C., June 1994, Method and apparatusfor treating stormwater.

U.S. Pat. No. 5,403,474, Emery, G. R., April 1995, Curb inlet gravelsediment filter.

U.S. Pat. No. 5,437,786, Horsley, S. W. et al., August 1995, Stormwatertreatment system/apparatus.

U.S. Pat. No. 5,480,254, Autry, J. L. et al., January 1996, Storm drainbox filter and method of use.

U.S. Pat. No. 5,549,817, Horsley, S. W. et al., August 1996, Stormwatertreatment system/apparatus.

U.S. Pat. No. 5,702,593, Horsley, S. W. et al., December 1997,Stormwater treatment system/apparatus.

U.S. Pat. No. 5,707,527, Knutson, J. H. et al., January 1998, Apparatusand method for treating stormwater runoff.

U.S. Pat. No. 5,730,878, Rice, T., March 1998, Contaminated waste watertreatment method and device.

U.S. Pat. No. 5,744,048, Stetler, C. C., April 1998, Clog resistantstorm drain filter.

U.S. Pat. No. 5,770,057, Filion, G., June 1998, Overflow water screeningapparatus.

U.S. Pat. No. 5,779,888, Bennett, P. J., July 1998, Filtering apparatus.

U.S. Pat. No. 5,810,510, Urriola, H., September 1998, Undergrounddrainage system.

U.S. Pat. No. 5,840,180, Filion, G., November 1998, Water flowsegregating unit with endless screw.

U.S. Pat. No. 5,890,838, Moore, Jr. Et al., April 1999, Stormwaterdispensing system having multiple arches.

U.S. Pat. No. 5,972,216, Acernese, P. L. et al., October 1999, Portablemulti-functional modular water filtration unit.

U.S. Pat. No. 5,985,157, Leckner, J. P. et al., November 1999, Filterdevice.

Previous vault or box type treatment devices used in wastewater orstormwater treatment applications acted as “flow-through” systems. Inthese previous devices, incoming flows enter the device, take a givenperiod of time based on baffles and size to flow through the device, andthen exit the device. If flows were coming in continuously, they wouldenter and exit the device at the same flow rate. Previous devices havedifferent systems within the vault to channel, divert, or reduce flowrates inside the vault in order to facilitate gravity separation. All ofthese devices are somewhat effective at settling out particles down to acertain size or specific gravity, but none of these devices areeffective at removing the very small size range of particles that makeup the majority of toxic pollutants in storm water runoff. Theseparticles are typically in the 100-micron and smaller size range, andsimply will not settle out of the water if there are horizontal flowvelocities present.

Most currently available stormwater treatment devices are designed toreduce the concentrations of pollutants in stormwater by screen, filteror enhanced gravitational separation (i.e. swirl concentrators).However, such systems provide little or no detention capture volume tomitigate the runoff peaks for small or large runoff events. In otherwords, these systems function as flow-through devices, resulting in thelack of capture volume and overall poor treatment performance.Specifically, much of the settleable materials trapped or depositedduring more numerous smaller runoff events are agitated and remobilized,and wash out of these devices when larger and more intense runoff eventsoccur.

Properly sized and maintained wet detention ponds (retention ponds)provide some of the most effective stormwater treatment available.Because of site-specific limitations, however many desirable features ofwet detention ponds are not utilized in real world conditions. Availablesurface area, possible thermal pollution, attractive nuisanceliabilities, mosquitoes and long-term maintenance access and disposalare some of the difficulties that must be addressed with a surface pond.

SUMMARY OF THE INVENTION

This stormwater mitigation system solves these problems and more, andincludes the benefits of a properly designed retention pond.

The apparatus advantageously settles particles down to a size of 100microns and smaller out of suspension in the stormwater by utilizing aunique volume control design. The vault of the present invention isdesigned to treat a given volume of stormwater runoff, as opposed to agiven runoff flow rate as treated in other devices. In so doing, thehorizontal flows for the entire volume of water to be treated can benearly eliminated, such that with a reduced flow rate very smallparticles may drop out of suspension and collect on the bottom of thevault. This is accomplished through a combination of physical space tocapture and hold water to be treated, restriction of flow out of theapparatus at a slower flow rate than flow into the apparatus, andvertically stacked pools of water with reduced or eliminated relativeflow velocity.

Features that are thought to provide such consistently high qualitytreatment advantageously include; a permanent pool (i.e., a poolessentially continuously present after it is first filled) to eliminatethe resuspension of pollutants, extended quiescent settling conditionsto promote retention of the Total Suspended Solids (“TSS”) and floatablematerials, subsurface conditions that curtail the resuspension ofdeposited sediment, sufficient volume to retain runoff from the majorityof runoff events and capture and treat the “first flush” of the largerevents, flow control system to attenuate the runoff flow rates from themajority of storm events and prevent flushing of the capturedpollutants, and large surface area that promotes oxygen transfer toreduce pollutant remobilization.

An aspect of this invention is to provide an apparatus for removal ofpollutants with densities greater than and less than water fromstormwater runoff.

Another aspect of this invention is to provide an apparatus that retainsand immobilizes trapped pollutants, even during periods when flows arehigh.

Another aspect of this invention is to accumulate pollutants that areless and more dense than water until a time when the apparatus iscleaned out.

Another aspect of this invention is to minimize velocity in the vicinityof the bottom of the apparatus to minimize resuspension of depositedsediments and associated pollutants. The slower the velocity of water inat least part of the device, the more effective will be the removal ofparticles.

Another aspect of this invention is to provide an apparatus that canprovide treatment of stormwater for larger tributary drainage areas byaddition of modular sections.

Another aspect of this invention is to collect stormwater runoff andrelease it at a controlled rate over a specified period of time via anoutflow opening.

Other aspects and advantages will become apparent hereinafter.

In one embodiment, the apparatus includes a by-pass manhole, apparatuschambers including a plurality of interior baffles, and a junction box.This apparatus, along with properly sized and installed ancillaryappurtenances, will advantageously collect and hold floatable debris,runoff bed load particulate material, free oil and grease, settleablesediments and those dissolved pollutants including metals, nitrogen andphosphorus nutrients, and soluble organic compounds the may adsorb oradhere to the surface of sediments and organic debris in stormwater.This apparatus, properly installed and utilizing a properly sizedoutflow opening aperture installed within an outlet opening, can captureand control the release of site runoff, significantly reducing erosionand stream degradation due to urbanization of the riparian habitat, andhelps restore pre-development runoff rates to urbanized areas.

In one embodiment, the apparatus is a below grade modular concretestormwater control device that is designed to manage and treatstormwater runoff by diverting a predetermined capture volume (or waterquality capture volume) into the apparatus. As would be understood byone of ordinary skill in the art, the capture volume is typically sized,for example, between the mean and the maximized runoff event as definedin “Urban Runoff Quality Management,” Water Environment Federation (WEF)Manual of Practice No. 23 and American Society of Civil Engineers”(ASCE) Manual and Report on Engineering Practice No. 87. The capturevolume is surcharged into detention storage (the active pool).

This capture is brought about by a volume control diversion weir thatdirects the design capture volume runoff into the apparatus with aminimum hydraulic loss into the apparatus. Any subsequent flow beyondthat of the design capture volume is allowed to bypass the apparatus viaa volume control diversion weir returning to the stormwater or runoffcollection system and/or receiving waters.

During wet weather and periods of site runoff, the detention time of thecapture volume may be optimized to promote quiescent sedimentationwithin the active pool whereby settable solid particles less than 100microns in size with a specific gravity greater than water will descendand insoluble oil droplets and marginally buoyant debris will float tothe surface.

One aspect of the invention is a rectangular chamber of variable length,width and height assembled in a modular fashion. The rectangular chambercontains a system of overflow and underflow baffles, both perpendicularto and oblique to the primary direction of flow from the inlet to thechamber to the outlet from the chamber, which are located at oppositeends of the rectangular chamber. The baffles in the chamber serveseveral purposes including: flow momentum and energy dissipation,creation of a tortuous flow path, retention and immobilization ofpollutants less and more dense than water, minimization of resuspensionof sediments, and minimization of remobilization of floatable pollutantsinto the water column. The primary process for pollutant removal isgravitational separation, which occurs while water is detained in thechamber.

A baffle configuration for minimization of resuspension of trappedsediments and associated pollutants was first conceptualized by theinventors and then optimized by iterative experimentation involvingthree dimensional velocity measurements and dye visualization for aplurality of baffle configurations using a geometrically andhydraulically scaled physical model. Baffle configurations wereevaluated for both dynamic (chamber filling and draining) andsteady-state (chamber full with inflow rate equal to outflow rate)conditions. This exhaustive experimentation indicates that the baffleconfiguration of the invention disclosed minimizes resuspension of fineand coarse sediments and associated pollutants to a degree that exceedsthe capabilities of prior art. In addition, a trapezoidal underflowbaffle, the shape of which was optimized during hydraulicexperimentation, impedes material less dense than water from enteringthe outflow section and exiting the vault. The trapezoidal configurationhas the advantage of decreasing the downward velocity of waterapproaching and then moving under the baffle and into the outlet sectionand, thereby, decreases the risk of entraining floatable pollutantstrapped behind the trapezoidal baffle into the flow passing into theoutlet section. As a result, the plurality of interior baffles and theweir configuration advantageously are designed to provide minimumre-suspension of settable solids from within the permanent pool.

In one aspect, the apparatus has an inlet that delivers water to thechamber from a tributary surface land area, either directly or via stormsewer system piping. Water entering the chamber passes through a systemof underflow and overflow baffles both perpendicular to and oblique tothe primary direction of flow from the inlet to the outlet, which islocated at the end of the rectangular chamber opposite the inflow. Aswater enters the chamber, the water level in the chamber rises above thepermanent pool water surface elevation, which normally is less than orequal to the elevation of the invert of the outflow opening. Outflowfrom the chamber is controlled by an opening that is sized to provide aspecified time for the water in the chamber to drain from the elevationat which the chamber is full to the elevation of the permanent pool.When the rate of inflow is greater than the rate of outflow, the waterlevel in the chamber will rise to the elevation at which the chamber isfull. Once the chamber is full, any flow in excess of the outflow rateunder full conditions will bypass the chamber via an overflow structure294. When the rate of outflow is greater than the rate of inflow, thewater surface elevation in the chamber will decrease at a ratecontrolled by the size of the outflow opening, and the water surfaceelevation will decrease to the elevation of the outflow opening invert,at which time outflow will cease. For convenience and brevity, thischamber inflow volume, as described in previous applications, is hereincalled a capture volume.

By slowly metering out storm runoff back to the external environment,the apparatus is of great benefit as it not only removes pollutants butalso duplicates runoff conditions that exist prior to urban development.This prevents erosion of stream channels, and also prevents a dischargeof rapidly flowing runoff that would simply pick up more sediment aftertreatment.

Another aspect of the invention is a stormwater treatment apparatus,including a receptacle adapted to receive water flowing from a surfacedrainage area, the receptacle having a bottom and a top, the receptaclehaving an inlet and an outlet, the inlet and the outlet being in fluidcommunication with one another; and at least one baffle positionedwithin the receptacle between the inlet and the outlet, the baffleextending from the bottom of the receptacle, a first portion of thebaffle and the bottom of the receptacle forming an angle therebetween.

A stormwater treatment apparatus varies from other types of treatmentapparatus, such as septic tanks, in that stormwater treatment apparatusmust capture a wide variety of particles of different sizes andcompositions in a pulsed hydraulics environment, as opposed to the moreconstant flow environment of a septic tank. A stormwater treatmentapparatus also differs from septic tanks in that the goal is topermanently trap sediments and other pollutants less or more dense thanwater, rather than to degrade organic matter and other biodegradablesubstances and in that a stormwater treatment apparatus is much largerthan septic tanks, desirably having a volume of at least 500 cubic feet,more desirably at least 600 cubic feet and, preferably, at least 750cubic feet. Generally, this apparatus size advantageously is sized toinclude an active pool volume sufficient to treat the capture volume ofthe area being treated. Additionally, one vault or more than one vaultmaybe used, depending on the topography of the area being treated, andsize of the vault(s) being used. Factors effecting the size and numberof vaults used in the apparatus, besides capture volume, includemanufacturing capability, transportability to site, modularity ofapparatus, cost of construction and installation, site topography, easeof installation, and apparatus footprint.

The apparatus advantageously substantially reduces bottom velocities,thereby greatly reducing resuspension of sediments. In particular, theangle formed between the first portion of the baffle and the bottom ofthe receptacle is desirably between 30 and 60 degrees, at is desirablyinclined in a downstream direction. Further, the height of the baffle isdesirably at least two feet to limit the washing out of sediment. Tofacilitate manufacture and cleaning the baffle desirably includes asecond portion, the second portion of the baffle extending from thebottom of the receptacle and forming an angle with the bottom of thereceptacle, the angle being roughly 90 degrees.

The apparatus desirably includes an inlet baffle positioned between theinlet and the outlet, the inlet baffle spaced from said bottom andextending between generally opposing walls and an outlet bafflepositioned between the inlet and the outlet, the outlet baffle spacedfrom said bottom and extending between generally opposing walls of thereceptacle. The lower end of the outlet baffle is desirably positionedbelow said outlet. The outlet baffle advantageously may define ahorizontal cross-section between a first baffle extending from saidbottom and said outlet baffle larger than the horizontal cross-sectionbetween said first baffle and a vertical plane tangent to an upstreamside of said outlet baffle. This has the effect of reducing the velocityof fluid. In this regard, it is desirable that outlet baffle defines acenter section and at least one outer section which extends toward saidoutlet from said center section. Advantageously, however, the spacesbetween the outlet baffle and the opposing walls are sufficiently largeto permit cleaning and to facilitate manufacture.

Yet another aspect of the invention is an apparatus for cleaningstormwater runoff, the apparatus including a vault having a top, abottom, two sides, a front and a back, the vault comprising a firstbaffle extending from the bottom of the vault; a second baffle extendingfrom the bottom of the vault, an inlet section having an opening and anoutlet section having an outlet opening.

The apparatus also advantageously includes vertically stacked columns ofwater, defined by, in one embodiment, varying horizontal flow rates andbounded by baffles creating regions of lower horizontal flow rate. Whenthe vault is filling or full, there is a column of water, called forconvenience an “active pool,” that is filling via the inlet, drainingvia the outlet, or both. This pool is the water being held, treated, andreleased by the invention. As the active pool is treated, sedimentssettle to the floor of the vault. As a result, when there is water inthe active pool, it has a significantly higher velocity than the waterin the permanent pool. A typical flow velocity for the active pool istwo to three feet per second.

In order to retain sediments and to prevent them from running out of thevault as it empties, and in order to prevent resuspension of thesediments as the vault refills at a later time, the apparatusadvantageously includes a permanent pool. The permanent pool sitsimmediately below the active pool and receives most or all sediments asthey drop out of the active pool. Due to the shape, design and spacingof the baffles surrounding and within the permanent pool and activepool, the permanent pool is an inactive pool (a permanent pool that hasminimal to no flow velocity.) Based on tests, the inactive permanentpool of the preferred embodiment of this invention maintains flowvelocities typically below 0.15 feet per second.

One of the failings of prior “flow-through” systems was their inabilityto settle small particles from smaller storm flows without resuspendingthose particles in later large storm flows due to turbulence andcurrents that reach all areas of the prior vaults. The presentapparatus, by creating an active pool that fills, holds and drainsimmediately above an inactive permanent pool, eliminates small particlere-suspension. Even in prior systems, simply applying baffles to createa physical barrier to sediments moving horizontally through the system,without creating a permanent pool, is only effective for larger, heavierparticles: in prior flow-through systems, smaller and finer particles,which form the majority of toxic pollutants, are left without aninactive permanent pool area to reside in and are simply suspended (orre-suspended) in the flow as it moves from compartment to compartmentand exits.

A further advantage of vertically stacked pools including a permanentpool is that of maintaining a compact footprint or plan area. By bothtreating the incoming volume of water and storing sediments in the sameplan area more water volume can be treated on a given site.

Finally, the present invention advantageously includes an overflowstructure, in one embodiment integral to the outlet section of thevault. When inflow of stormwater exceeds the volume capacity of thetreatment system, the overflow structure diverts excess stormwater flowwithout substantially effecting the ability of the system to effectivelytreat the full volume of stormwater already in the vault.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of this invention, the best mode, is illustrated in theattached drawings, in which like numerals indicate like componentsthroughout the several views. Views include:

FIG. 1—a plan (from a perspective above the apparatus) view of theapparatus that is the subject of this invention;

FIG. 2—a profile (side elevation) view of the apparatus;

FIG. 3—a cross-sectional view of the inlet section of the apparatus(cross-section 1—1 shown on FIG. 1 and FIG. 2);

FIG. 4—a cross-sectional view of the outlet section of the apparatus(cross-section 2—2 shown on FIG. 1 and FIG. 2);

FIG. 5—a detailed (enlarged) profile view of the inlet section baffleconfiguration;

FIG. 6—a detailed plan view of the outlet section

FIG. 7—a detailed view of the outflow opening configuration;

FIG. 8—an illustration of baffle spacing for this invention for even andodd numbers of chambers for a multi-chambered apparatus (the number ofmidsections depicted in this view, four for the even illustration andfive for the odd illustration, are specific examples of the generalizedodd and even baffle spacing rules and are not intended to berestrictive);

FIG. 9—an illustration of a modified embodiment of the presentinvention, including an external bypass structure;

FIG. 10—an illustration of the apparatus, in one embodiment,incorporating a gravity dynamic flow control orifice; and,

FIG. 11—a detail plan view of the apparatus, in one embodiment,incorporating an integral overflow bypass structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The drawings illustrate one embodiment of an apparatus 100 forseparation of pollutants that are less and more dense than water fromstormwater runoff. Referring to FIG. 1 and FIG. 2, the apparatus 100consists of a top 140, a bottom 160, an inlet end 170, an outlet end150, a left side 300, and a right side 310 (left and right are relativeto the view from the inlet end 170 to the outlet end 150). These sidesdefine a rectangular chamber with an inlet section 110, an outletsection 120, and one or more midsections 130.

The length of the most basic configuration of the apparatus 100 isdesirably at most 20 ft, more desirably at most 18 ft 6 in, and, mostpreferably, 17 ft 6 in (inside dimension); and the width of theapparatus id desirably at most 10 ft, more desirably at most 8 ft 6 in,and, most preferably, 7 ft 6 in (inside dimension); the height of theapparatus is 6 ft or 8 ft (inside dimensions). Outside dimensions andinside dimensions may vary due to structural strength requirements ofthe apparatus 100. Desirably, the length of the apparatus 100 increasesin 4-ft, 8-ft, or 16-ft increments as additional midsections 130 areemployed. The top 140 and bottom 160 are desirably parallel to eachother and are separated by a distance of 6-ft or 8-ft (insidedimensions). The left side 300 and right side 310 are desirably parallelto each other and are separated by a distance of at most 10-ft, moredesirably 8-ft 6-in and, preferably, 7-ft 6-in (inside dimensions). Theinlet end 170 and the outlet end 150 are desirably parallel to eachother and, for the most basic configuration, are desirably separated bya distance of at most 20-ft and, more desirably, 17-ft 6-in (innerdimension). The distance between the inlet end 170 and the outlet end150 desirably increases by 4-ft, 8-ft, or 16-ft increments as additionalmidsections 130 are employed. The thickness of the inlet end wall 170,the outlet end wall 150, the left side 300, the right side 310, and thebottom 160 is desirably at least 3-in and, preferably, 6-in or more. Thethickness of these walls may increase or decrease as structural needs ofan installation dictate. The thickness of the top 140 of the apparatus100 is at least 3-in and, desirably, 6-in or more but may increase ordecrease as structural needs of an installation dictate.

Based on experience gained after the filing of the original application,it is currently believed that the preferred dimensions for the apparatusare a length of about eighteen feet (along the longest dimension of theapparatus), a width of about eight feet, and a depth of about eightfeet. As the apparatus is made larger, though, it advantageously cantreat a larger capture volume of stormwater. The preferred method ofincreasing the size of the apparatus is to add modular midsections toincrease the length and treatment capacity of the apparatus. Desirably,the apparatus can thus range from a basic configuration of abouteighteen feet in length to compound, large configurations ofapproximately one hundred feet in length including a plurality ofmidsections. As topographical, footprint, transportation, manufacturingand capture volume requirements change, these structural dimensions maysimilarly change.

The ability to increase the size and treatment capacity of the apparatus100 by addition of modular midsections 130 is advantageous formanufacturing since the apparatus 100 can be manufactured in a widerange of incremental sizes using the same set of forms for precasting.In addition, the modular construction is favorable for applicationsrequiring a large apparatus 100 as the modular sections 110, 120, and130 can be transported on one or more trucks and then assembled on-site.The incremental sizing may be advantageous for performance at improvingwater quality as well when the apparatus 100 is sized according tomanufacturer's recommendation. For example, if a user, based on sizingcalculations, determines that the required capacity of the apparatus 100necessary to achieve a desired performance is equivalent to the capacityof a midsection with a length of 11-ft, then the user would specify that2 midsections 130 are needed, one 8-ft long and the other 4-ft long (ortwo 8-ft long sections), since midsections 130 are discrete componentsand 1 mid-section 130 would not provide the required capacity. As aresult of this modular, incremental sizing, the apparatus 100 specifiedby the user would always have a capacity equal to or in excess of thatrequired and would, therefore, provide a minimum degree of desiredtreatment.

A plurality of baffles 220 and 250 are positioned between the inlet end170 and the outlet end 150. The primary direction of flow is defined asthe direction from the inlet end 170 toward the outlet end 150 in thehorizontal plane. In the disclosed embodiment, the primary direction offlow is perpendicular to the inlet end 170 and the outlet end 150 andparallel to the top 140, bottom 160, left 300, and right 310 sides.There are two types of overflow baffles employed in this invention.These baffles are referenced as components 220 and 250. Component 220 isa hybrid baffle, and component 250 is an angled baffle. The results ofextensive hydraulic testing indicate that the baffle configurationillustrated, as well as the claimed baffle configurations using variouscombinations of hybrid 220, vertical, and angled 250 baffles, is highlyeffective at minimizing resuspension of trapped sediments and associatedpollutants. Velocity measurements and dye visualization experimentsindicate that the apparatus 100 disclosed herein provides a degree ofreduction of resuspension that significantly surpasses that of existingart.

Referring to FIG. 1, FIG. 2, and FIG. 5, the hybrid baffle 220 consistsof a vertical section 240 that is perpendicular to the primary flowdirection and an angled section 230 that is oblique to the primarydirection of flow, forming an angle, α, with the horizontal plane (angleα is depicted in FIG. 5). Preferably, the vertical baffle section 240has a length of 1-ft and the angled section of the baffle 230 rises fromthe top of the vertical section 240 at a 45° angle for a distance of1-ft in the horizontal plane and a distance of 1-ft in the verticalplane. Preferably, the total vertical rise for a hybrid baffle 220 is2-ft from the chamber bottom 160, and the horizontal projection is 1-ft3-in. in the downstream direction (including thickness of the verticalsection 240). An angle other than 45° may be used for the hybrid baffle220 as long as the lengths of components 230 and 240 are adjusted toprovide a total rise of 2-ft and the downstream end of component 230does not extend beyond the dimensions of the top 140, bottom 160, andwalls 300, 310, and 170 of the precast unit containing the baffle.Desirably, the angle α is between 0° and 90°, and, more desirably,between 30° and 60° degrees.

The angled baffle 250 rises 2-ft from the bottom of the chamber 160. Anangled baffle 250 is illustrated in FIG. 1 and FIG. 2 in plan andprofile views, respectively. For the best mode, the baffle 250 forms anangle, α, of 45° with the chamber bottom 160. An angle other than 45°may be used, provided that a vertical rise of 2-ft is maintained andthat the downstream end of the angled baffle 250 does not project beyondthe end of the associated 8-ft midsection 130. Hybrid baffles 220 andangled baffles 250 may be interchanged to create numerous embodiments;however, the best mode utilizes a single hybrid baffle 220 in the inletsection 110 and angled baffles 250 in midsections 130, the spacing ofwhich is described below. Other shapes and heights of baffles, up to thefull depth of the permanent pool have been tested and are viablealternates to the “best design” shown herein and are part of the designclaims of this apparatus 100.

Extensive hydraulic experimentation and testing of baffle configurationsand types was conducted to determine baffle geometry that effectivelyreduced velocities in the lower section of the apparatus 100 wheresediments accumulate after settling out of the water. As will beappreciated by one of skill in the art, the creation of this reducedvelocity region results in a region of little or no velocity near thegravitational bottom of the vault. That is, this region comprises aninactive permanent pool. Initial testing indicated that angled baffles250 were more effective than vertical baffles at decreasing bottomvelocities in the apparatus' midsections 130. The inventors initiallytested angled baffles 250 for the purpose of examining the effect of theangled baffles 250 on flow passing over the crest of the angled baffles250. In the process of this experimentation, the inventors discoveredthat the angled baffles 250 had a favorable effect on bottom velocitiesbetween two angled baffles 250 separated by a distance of 16-ft or less.A hybrid baffle 220 was developed and tested for the purpose ofachieving a reduction in bottom velocities in the midsections 130comparable to that found using an angled baffle 250, while at the sametime decreasing the length in the horizontal plane consumed by theangled baffle 250 by a distance equivalent to the product of the heightof the vertical portion of the baffle 240 and the tangent of the angle90°−α. This reduction in the horizontal distance required to accommodatethe hybrid baffle 220 allows the inlet section 110 to be shortened,resulting in a reduction in the amount of material necessary tofabricate the inlet section 110. In addition, the vertical portion 240of the hybrid baffle 220 has the advantage of improved access for a hoseor vacuum to clean out the area beneath the baffle 220. An angled baffle250 permits access beneath the baffle 250 for cleaning only where thedistance between the under-surface of the baffle 250 and the bottom ofthe chamber 160 (inside dimension) is greater than the diameter orheight of the intake component of the vacuum or pumping cleaning system.For both angled 250 and hybrid 220 baffles, the experimentationconducted indicated that both types of baffles 250 and 220, performedvery well at evenly distributing flow across the width of the apparatus100.

Water is supplied to the apparatus inlet section 110 via an inlet pipeor other conveyance 180 carrying water from the tributary drainage areato the inlet of the apparatus 190. The invert of the inlet aperture 190is desirably at least 3-ft above the chamber bottom 160 (insidedimension). The apparatus 100 may also receive water from the tributarydrainage area directly rather than via an up-gradient, piped storm sewersystem. An example of this configuration would be an apparatus 100installed to receive water from a manhole chamber below a curb-side dropinlet.

The inlet section 110 consists of several distinct components that areshown in FIG. 1, FIG. 2 in plan and profile views, respectively. FIG. 3shows a cross-section (1—1) of the inlet section 110, and FIG. 5 showsdetails of the baffle configuration for the inlet section 110. Thedimensions of the inlet section 110 are defined by the inlet end wall170; the top 140, bottom 160, left 300, and right 310 sides; and a planeperpendicular to the primary direction of flow located a prescribeddistance from the inside dimension of the inlet end wall 170 in thedownstream direction. This prescribed distance is defined by the lengthdimension of the precast segment containing the energy dissipationbaffle 200 and the most upstream hybrid 220 or angled 250 baffle and,most preferably is 4-ft 9-in. The dimensions of the inlet section 110,exclusive of baffles, desirably are equivalent to the dimensions of theoutlet section 120, providing the advantage of having the capability tocast inlet 110 and outlet 120 sections using the same form. The inletsection 110 desirably includes a manhole 135 for access to the inletsection 110 for maintenance. The cover of the manhole 135 is desirablyvented to allow exchange of air between the inside of the apparatus 100and the surface atmosphere to prevent anoxic conditions from developingin the permanent pool. The permanent pool is defined as the volume ofwater and trapped pollutants in the apparatus 100 above the bottom ofthe chamber 160 and below the invert of the outflow opening 280.

A component of the inlet section 110 is a flow energy dissipation baffle200 that is perpendicular to the primary direction of flow. The energydissipation baffle 200 is parallel to the inlet end wall 170 and ispositioned so that the side of the energy dissipation baffle 200 facingthe inlet wall 170 is desirably at most 1-ft 6-in and preferably 1-ftfrom the inner side of the inlet end wall 170 in the primary directionof flow. The energy dissipation baffle 200 desirably is connected to theleft side 300 and right side 310 from a distance of desirably at most2-ft and preferably 1-ft 6-in above the chamber bottom 160 (insidedimension) to a distance of desirably at most 1-ft, and preferably 6-infrom the chamber top 140 (inside dimension). The energy dissipationbaffle 200 desirably has a thickness of 3-in. The purpose of the flowenergy dissipation baffle 200 is to decrease the energy of the incomingflow. For the apparatus 100 described herein, the decrease in flowenergy translates to a decrease in the velocity of the incoming water.The space 210 is provided between the top of the energy dissipationbaffle 200 and the top 140 of the apparatus 100 for the purpose ofallowing overflow for high flows and for the purpose of providing accessfor maintenance. Hydraulic testing indicates that the energy dissipationbaffle 200 is effective at decreasing flow energy. The inventorsexamined several options for spacing between the inlet end wall 170 andthe flow energy dissipation baffle 200 and found that theabove-described spacing provided a good balance between theeffectiveness of energy dissipation and the space necessary to accessthe area between the inlet end wall 170 and the baffle 200 formaintenance.

Another element of the inlet section is the inlet overflow baffle 220.The inlet overflow baffle 220 is a hybrid baffle (described above). Theinlet overflow baffle 220 desirably is connected to the chamber bottom160 and the left 300 and right 310 sides of the chamber so that watercan only pass over the top of the baffle, defined by component 230. Thevertical portion 240 of the inlet overflow baffle 220 desirably islocated a distance of at least 2-ft 6-in, more desirably at least 3-ft,and preferably 3-ft 6-in from the inlet end wall 170 (insidedimensions). The thickness of the inlet overflow baffle 220 is desirably3-in. The vertical rise for the inlet overflow baffle 220 is desirablyat most 3-ft, more desirably at most 2-ft 6-in, and, preferably, 2-ft,and the horizontal distance in the direction of flow is desirably atmost 2-ft, more desirably at most 1-ft 6-in, and, preferably, 1-ft 3-in(including the baffle thickness of 3-in) for the best mode.

A midsection 130 of the apparatus 100 is defined by a top 140, a bottom160, a left 300, and a right 310 side that desirably are connected at90° angles to form an open-ended rectangular section. FIG. 1 and FIG. 2depict an apparatus 100 with two, 8-ft midsections 130. The apparatus100 desirably has at least one midsection 130 but may have additionalmidsections 130. Desirably, the midsections 130 have a length of 16-ft,more desirably 4-ft, and, preferably, 8 ft. Angled baffles 250 desirablyare spaced at 4-ft increments, more desirably at 8-ft increments, and,preferably, at 16-ft increments in midsections 130. For midsections 130requiring angled baffles 250 to achieve this spacing, an angled baffle250 (described above) is attached to the bottom of the midsection 130 sothat the downstream tip of the angled baffle 250 coincides with the endof the midsection 130. Such an angled baffle 250 in a midsection 130 isshown in FIG. 1 and FIG. 2 in plan and profile views, respectively.While an angled baffle 250 desirably is used in the midsections 130,vertical, hybrid, or other baffle shapes 220 may be used. Since baffle220 and 250 spacing is preferably 16-ft and midsections 130 are added in4-ft, 16-ft, or 8-ft increments, not all midsection segments 130 willneed baffles 220 and 250. FIG. 8 illustrates baffle 220 and 250 spacing.As FIG. 8 indicates, baffles 220 and 250 preferably are spaced every16-feet, and a baffle 220 and 250 is desirable at the end of the mostdownstream midsection 130. Therefore, for an even number of midsections130, desirably with a length of 8-ft (four as an example in FIG. 8), alloverflow baffles 220 and 250 are preferably spaced 16-feet apart. For anodd number of midsections 130, desirably with a length of 8-ft, (five asan example in FIG. 8), however, spacing is preferably 16-feet betweenall overflow baffles 220 and 250 with the exception of the spacingbetween the penultimate and ultimate downstream baffles 220 and 250 atthe end of the most downstream midsection 130. The number of midsections130 depicted in FIG. 8 are shown as examples of even and odd numbers ofmidsections 130 and should not be interpreted as restrictivespecifications. Each midsection 130 desirably will have a manhole 135,allowing access through the top of the chamber 140 for maintenance.Desirably, all manholes 135 will be vented to prevent development ofanoxic conditions in the permanent pool and will be of sufficient sizeto allow the contents of the apparatus 100 to be pumped out as a part ofregular maintenance. Manholes 135 positioned above midsections of theapparatus 100 desirably will have a collar 145 with approximately thesame inner diameter as the manhole that extends into the chamber 3-inbelow the top 140. The purpose of the collar 145 is to limit the surfacearea of the water and associated floatable pollutants in the chamberthat could potentially be forced out of the apparatus 100 via vents inmanhole access areas 135 when the apparatus 100 fills completely.

The midsection 130 components of the apparatus 100 are the primarytreatment and pollutant collection chambers. During the time that wateris detained in the apparatus 100, sedimentation occurs, resulting indeposition of sediments and associated pollutants with densities greaterthan water on the bottom 160 of the midsections 130. The configurationof baffling 220 and 250 is such that sediments deposited on the bottom160 of the midsections 130 resist resuspension during subsequent runoffevents. Once the thickness of the sediment layer on the bottom 160 ofthe midsections 130 increases to a prescribed depth, the apparatus 100is cleaned via a pump-out or other method to remove the permanent pooland trapped pollutants from the apparatus 100 for disposal.

In addition to sediment removal, the midsections 130 of the apparatus100 collect and retain materials less dense than water. During the timethat water is detained in the apparatus 100, materials that are lessdense than water rise toward the water surface. Since flow from themidsections 130 passes to the outlet section 120 by flowing beneath thetrapezoidal baffle 260, pollutants on the water surface in themidsections 130 are retained on the upstream side of the trapezoidalbaffle 260. Due to the elevation of the invert of the outlet opening280, the surface of the permanent pool in the apparatus 100 desirablyremains at least 1-ft above, and, preferably, 1-ft 5-in above thehighest elevation at which water can pass below the trapezoidalunderflow baffle 260. As described below, the trapezoidal geometry ofthe underflow baffle 260 is advantageous for prevention of entrainmentof pollutants collected on the surface of the mid-sections 130 into theflow beneath the trapezoidal baffle 260 entering the outlet section 120.Desirably, a mat or mats composed of material capable of absorbingpetroleum-based hydrocarbons with densities less than that of water willbe placed in the midsections 130 of the apparatus 100 for the purpose ofimmobilizing these pollutants. Manholes 135 will be large enough topermit removal of the absorbent mats.

A detailed plan view of the outlet section 120 is shown in FIG. 6, and adetail of the outflow opening configuration 280 is shown in FIG. 7. Thedimensions of the outlet section 120 are defined by the outlet end wall150; the top 140, bottom 160, left 300, and right 310 sides; and a planeperpendicular to the primary direction of flow located 4 ft 9 in fromthe inside dimension of the outlet end wall 150 in the upstreamdirection. The dimensions of the outlet section 120, exclusive ofbaffles, are equivalent to the dimensions of the inlet section 110,providing the advantage of having the capability to cast inlet 110 andoutlet 120 sections using the same form.

One component of the outlet section 120, is a trapezoidal underflowbaffle 260. In the plan view (FIG. 1 and FIG. 6), the trapezoidalunderflow baffle 260 desirably consists of a center segment parallel tothe outlet end wall 150 and a pair of outer segments. The center segmentis located desirably at least 2-ft, more desirably 3-ft, and, preferably4-ft from the outlet end wall 150 (inside dimension of end wall toupstream side of trapezoidal baffle 260). The center segment of thebaffle 260 is centered with respect to the left 300 and right 310 sidesof the chamber. Preferably, the length of the center segment 260 is 1-ftand, as a result, the distance between the ends of the center segment ofthe baffle 260 and each wall 300 and 310 is 3-ft 3-in. In the plan view,the trapezoidal baffle extends from the ends of the center segment tothe corners defined by the intersection of the left side wall 300 andthe outlet end wall 150 and the right side wall 310 and the outlet endwall 150. In the profile view (FIG. 2), the trapezoidal baffle 260 islocated so that the bottom of the baffle 260 desirably is at most 1-ft11-in and, preferably, 1-ft 6-in above the bottom of the chamber 160(inside dimension). The baffle 260 extends to the top of the chamber 140and is joined to the top of the chamber 140 along the trapezoidal-shapedtop edge of the baffle 260 displayed in the plan view (FIG. 1 and FIG.6). The trapezoidal underflow baffle 260 desirably is also attached tothe sides of the apparatus 100 where the left and right sides 300 and310, respectively, form corners with the outlet end 150 from a distance,preferably, 1-ft 6-in above the bottom of the chamber 160 (insidedimension) to the top of the chamber 140.

Initially, the inventors tested a simple, vertical underflow baffle witha thickness of 3-in that was positioned in a plane entirelyperpendicular to the outlet end wall 150. This incarnation of theunderflow baffle was located a distance of 4-ft from the outlet end wall150 (inside dimension of end wall to upstream side of underflow baffle)and resulted in an area of 5.625 ft² between the downstream end of theangled baffle 250 and the upstream side of the underflow baffle in theplan view (see FIG. 1). The inventors investigated the trapezoidalunderflow baffle 260 of the present invention for the purpose ofdecreasing the velocity of the flow passing through the plane betweenthe downstream end of the angled baffle 250 and the upstream side of theunderflow baffle 260 in the plan view. The area in the plan view betweenthe downstream end of the angled baffle 250 and the upstream side of theunderflow baffle 260 is preferably 18.625 ft². Comparison of the areasbetween the underflow baffle and the upstream angled baffle 250 for thevertical underflow baffle configuration and the trapezoidal underflowbaffle 260 configuration indicates that for equivalent rates of flowpassing between the upstream angled baffle 250 and the underflow baffle,the velocity for the vertical baffle configuration preferably would be3.3 times greater than the velocity for the trapezoidal baffle 260configuration. The lower velocity attained using the trapezoidal baffle260 configuration of the present invention is advantageous forprotection from entrainment of pollutants residing on the surface layerof the midsections 130 into the flow from the midsection 130 to theoutlet section 120. Desirably, the angle between the center segment ofthe baffle and the outer segments of the baffle is between 90° and 180,more desirably between 120° and 160°, and, preferably 130°.

Another component of the outlet section 120 is outlet screening 270which is designed to keep trash and/or debris from clogging the outletopening 280. The outlet screening 270 consists of fine screening or afine mesh configured as a semi-circle, arch, rectangle, or straightscreen in front of the outflow opening 280. The screening is attached tothe outlet end wall 150 a horizontal distance in front of the outletopening that is proportionate to the outlet opening size, but no lessthan 2 times the diameter of the outlet opening and to the bottom 160and top 140 of the chamber so that all water passing through the outflowopening 280 will have first passed through the screening 270. Thescreening 270 will be attached in a manner that will permit removal andcleaning of the screening via an access manhole 135 located in the topof the outlet section 120. The cover for the manhole 135 will be ventedto allow exchange of air between the inside of the apparatus 100 and thesurface atmosphere to abate development of anoxic conditions in thepermanent pool and to relieve air pressure as the apparatus fills anddrains with water.

The outflow opening 280, shown in FIG. 1, FIG. 2, and FIG. 4 is thedevice controlling the release of water from the apparatus 100. A detailof the outflow opening 280 components is shown in FIG. 7. The outletdesirably consists of an 8-in diameter pipe 290, desirably extendingfrom 3-in upstream of the outlet end wall 150 (inside dimension),through the outlet end wall 150. The end of the pipe 290 that is insidethe apparatus 100 desirably is covered with an 8-in cap 282. An opening280 that is sized to provide a predetermined time for the water in thechamber to drain from the elevation at which the apparatus 100 is fullto the elevation of the permanent pool is machined into the 8-in cap282. The opening 280 is manufactured so that the lowest point of theopening is preferably at least ½-in above the lowest point of the 8-inpipe 290 at the end where the cap 282 is attached.

An advantage of creating the outflow opening aperture 280 in a cap 282that is placed over the end of the outflow pipe 290 that is inside theoutlet chamber is that the opening size can be changed as desired duringmaintenance by replacing the cap 282 with another cap 282 with adifferent sized opening 280. This flexibility in opening 280 sizing isadvantageous for providing an apparatus 100 that can provide an array oftreatment levels. The opening aperture size 284 dictates the time thatwater is detained in the apparatus 100. A smaller opening aperture size284 would result in detention of water for a longer period of time thanthat afforded by a larger opening size. The treatment efficiency of anapparatus 100 will increase as the time that water is detainedincreases. Therefore, the level of treatment can be adjusted byincreasing the opening size (decreasing the level of treatment) ordecreasing the opening size (increasing the level of treatment). Anotheradvantage of the outflow opening configuration 280, is that thepositioning of the opening invert, preferably, a distance of 2-ft 11-inabove the bottom 160 and downstream of all baffling 200, 220, 250, and260 results in release of water with the lowest sediment concentrationsthrough the opening 280. An outflow opening 280 positioned lower thanthat in the illustrated embodiment would draw more water from the lowerpart of the outlet section 120, which would contain more suspendedsediments. An outflow opening 280 positioned higher than that in theillustrated embodiment would result in a greater permanent pool volumethat would need to be pumped out during maintenance.

The apparatus, being an off line type below grade structural stormwatercontrol device, in one embodiment manages the recommended capturevolume—sized for a mean runoff event following the sizing criteria asoutlined in, for example, the “Urban Runoff Quality Management”, WEFManual of Practice No. 23, and ASCE Manual and Report on EngineeringPractice No. 87 or other source known to one of ordinary skill in theart.

Storm events are, in one embodiment, handled by diverting thatpercentage of stormwater events from the site storm drainage collectionsystem. The apparatus advantageously provides adequate time for thecapture volume within the active pool for pollutants with specificgravities of lesser or greater than water to be captured within thehydraulically designed plurality of baffling within the permanent pool(i.e., permanent pool), reducing sediment resuspension, retainingfloating debris and hydrocarbons, and trapping neutrally buoyant trash.

As known to one of ordinary skill in the art, a mean runoff event istypically defined, for example, as the event resulting from the “meanstorm precipitation depth, which is the depth of all runoff-producingstorms (total precipitation of 2.5 mm or 0.10″ or more) from a long-termprecipitation record for a given location, using a six-hour separationto define each storm event. This “mean storm event capture volume” willtypically result in the capture of roughly 70% of all runoff-producingevents in their entirety or approximately a “two-year storm,” defined asa stormwater event that occurs on average once every two years, orstatistically has a 50% chance on average of occurring in a given year.Other methods for determining the capture volume can similarly beemployed, depending on site requirements.

FIG. 9 illustrates one embodiment of the present invention, including anexternal bypass structure. In this embodiment, the apparatus 100 inflowrate is controlled by a site-specific designed control weir 410 housedwithin a bypass manhole 400 of the type well-known to those of ordinaryskill in the art. Influent enters the system from a drainage system, aswell known to one of skill in the art, from a sewer system main or, forexample, an inflow pipe 184. The properly sized weir 410 diverts thesite runoff into the apparatus 100 through the apparatus influent pipe180. Bypass pipes 430 divert excess water volume beyond the maximumcapture volume by diverting excess water volume over the control weir410 and through the bypass pipes 430. The bypass manhole 400 istypically accessed by an access manhole 135.

The energy dissipation baffle 200 is so located to diffuse and create alaminar flow of the turbulent high velocity stormwater runoff on entryinto the apparatus 100. The baffle is angled to extend toward the frontof the vault as it extends downward. The reduced energy stormwater isdiverted in less turbulent lower velocity downward against the bottom ofthe apparatus 100, and under the energy dissipation baffle 200 to bedirected upward by the hybrid baffles 220. The capture area between theenergy dissipation baffle 200 and the inlet end wall provides an areafor the capture and retention of the larger and more buoyant trash anddebris, as known in the art, in a forebay trash compartment 440. Thistrash area is accessed via a manhole 135 for subsequent collection andremoval of sequestered debris via vacuum suction lift or othermechanical means. Advantageously, the forward angled energy dissipationbaffle 200 permits easy access via the manhole 135 while providingadditional energy dissipation.

The hybrid-baffles 220 (including, for example, 230, 240 and 250) are solocated with respect to the energy dissipation baffle 200 to direct theinitial and subsequent stormwater inflow in an upward direction therebyproviding a laminar flow pattern in the active pool 450 reducing theturbulence in the inactive permanent pool 460 to near zero, thuspreventing resuspension of previously settable materials. The availableactive pool 450 above the permanent pool 460 provides a verticallystacked water column desirably sized to accommodate the design capturevolume.

This ability to exploit the vertically stacked water columnconfiguration provided by the preferably rectangular design of theapparatus 100 enhances the ability to capture stormwater runoff from asite. By simply selecting the appropriate water volume, the apparatus100 can significantly reduce erosion and stream degradation fromincreased flows due to urbanization and help restore pre-developmentrunoff rates. Due to an effective stacked water column volume control,the apparatus has superior pollution removal and retention capabilitiesthe apparatus advantageously mitigates downstream erosion and riparianhabitat degradation through retaining and slowly metering out thecapture volume, through the properly sized outflow opening aperture 284installed within outlet opening 280, flow from each event.

Intermediate angled baffle(s) 220 are so arranged to provide optimumvolume and sediment control spacing by maintaining the upwarddirectional stability of the stormwater inflow. These sediment controlbaffles 220 advantageously provide an uninterrupted quiescent area ofcapture volume to sequester settable solids and pollutants, reducing theprobability of resuspension during the introduction of stormwater intothe apparatus. The longitudinal spacing of the angled baffle(s) 220 ispreferably optimized to provide a minimum of one manhole 135 access forevery approximately 64 square feet of pollutant capture area forsubsequent collection and removal of sequestered sediment andhydrocarbon material via vacuum suction lift or mechanical means. In oneembodiment, the minimum size for the bypass manhole 400 is typicallyaround 36″ by 36″ square or, alternatively, 48″ inside diameter. Theretypically is a 30″ minimum spacing between the bypass manhole 400,outlet box 470 and the main tank 480 of the apparatus 100 to allowsufficient space for the installation and sealing of influent connectionpipes 180 and effluent connection pipes.

As known to one of ordinary skill in the art, the influent connectionpipes 180, effluent connection pipes 290, and bypass pipes 430 aretypically supplied and cut to proper length depending on the topography,flow, and specific requirements of a particular site. Similarly, thedimensions of the apparatus will vary based on site requirements.

The decant period or drain down time is optimized to allow for thegravity separation of pollutants with either a specific gravity lessthan or greater than water. The retention time of the capture volume inthe stacked water column provides a quiescent period for enhancedsettling, and is consistent with recommendations shown in “Removal Ratevs. Detention Time for Stormwater Pollutants as defined in“Effectiveness of Extended Detention Ponds” authored by Grizzard et al.,1986 or other similar period recommendations as commonly known to thoseof skill in the art.

In one embodiment, the process capture volume stormwater flow rate ismetered by a fixed aperture orifice 280 to insure proper retention ofthe capture volume and regulate maximum discharge flow rate. In oneembodiment, a flow control orifice may be, for example, mounted in asealed outlet tee fitting with a standpipe 490 top rim at such elevationto prevent flow “short circuiting” at maximum water levels.

The orifice 280 is desirably protected from neutrally buoyant materialby a removal screen 270, which desirably typically includes a minimumnet opening area of about 25 to 50 times the opening of the orifice, andpreferably about 35 times the opening of the orifice. The orifice 280,standpipe 490, and screen 270 are preferably constructed of non-metallicnon-corrosive materials.

FIG. 10 provides an illustration of the apparatus, in one embodiment,incorporating a dynamic flow control orifice.

Unlike previous devices, the dynamic flow control orifice system 500 isa moveable orifice that differs from all other previous devices, as itsprimary purpose is to control the time for outflow of stormwater fromsaid stormwater mitigation system, by maintaining a constant dischargerate throughout a majority of the discharge volume without utilizing anyoutside mechanical or electrical force or power. The dynamic flowcontrol orifice system 500 does so by utilizing a properly sized andlocated orifice 510 within a buoyant floatation collar 520 protectedfrom surface contamination via a solid shield 530 and from neutrallybuoyant materials by a screen 540. A combination of gravity and buoyancythus keeps the dynamic flow control orifice system at an advantageousposition in the apparatus without outside influence, while the height ofthe orifice 510 is adjustable relative to the water surface by adjustingthe vertical distance between the orifice 510 and the flotation collar520. The vertical adjustment of the orifice 510 advantageously maintainsthe predetermined discharge flow rate through the great majority ofretained capture volume. The action arm 550 is typically pivoted on anon-mechanical swing joint 560 to arc through the entire vertical rangeof the retained capture volume, and permits the orifice to move with thewater level. By comparison, a fixed outlet orifice 280 as shown in FIG.9, for example, typically does not move with the vault water level.

The preferred construction material for this component is synthetichydrophobic material with non-corrosive fasteners, however, any suitablematerial such as plastic, fiberglass, and the like are to be consideredincluded within the description and application of this apparatus. Thesimplified gravity dynamic flow control orifice described presentlyherein can advantageously be applied to any water treatment system,including the embodiments described herein and other systems known toartisans of ordinary skill in the art.

FIG. 11 provides a detailed plan view of the apparatus, in oneembodiment, incorporating an integral overflow bypass structure. In oneembodiment, this stormwater treatment apparatus is an integrated systemwhereby the above mentioned bypass manhole 400, volume control weir 410and junction box 470 are combined and advantageously made integralwithin the confines of the stormwater treatment apparatus itself, as atypically unitary below grade modular precast concrete stormwatercontrol and treatment device that is designed to manage and treatstormwater runoff by diverting the design water quality capture volumeinto the apparatus as a surcharged detention storage volume defined asthe active pool and controlled release of said capture volume, withsediments stored in the permanent pool. The preferred constructionmaterial for all structural components is precast concrete however, anysuitable material such as plastic, fiberglass, steel, cast in placeconcrete, and the like are applicable to this apparatus.

The integral bypass structure apparatus utilizes a novel, properly sizedintegral weir appurtenance 410 to divert the predetermined designcapture volume water volume into the modular apparatus 100 from astormwater collection system connected by, for example, a collectionsystem inflow pipe 184. This capture of the capture volume is broughtabout by a integral volume control diversion weir 410 that directs thedesign runoff into the apparatus through the apparatus inflow pipe 180,with a minimum hydraulic loss into the apparatus 100. Any subsequentflow beyond that of the design capture volume is allowed to bypass theapparatus 100 via the integral volume control diversion weir 410returning to the stormwater or runoff collection system or receivingwaters through a collection system outflow pipe 292. Stormwater treatedby the apparatus is returned via a discharge pipe 280 to the combinationjunction box 470/bypass manhole 400 for return to the stormwater orrunoff collection system or receiving waters through the collectionsystem outflow pipe 292.

In one embodiment the integral bypass system is preferably configuredwith the apparatus 100 aligned perpendicular to the collectionstormdrain that is to be intercepted. The bypass headworks isadvantageously configured to provide a minimum footprint, throughintegration of the bypass manhole 400 and junction box 470 with theentire apparatus, while allowing for a trash and debris collectionassembly to be incorporated into the integrated apparatus treatmenttrain. The size of the bypass headworks 400, junction 470 and integralweir 410 elevation relative to the apparatus is typically established bythe maximum design flow rate in the collection stormdrain that is to beintercepted. The headworks size typically corresponds to the minimumrequired for the integral weir 410 size, location and materials of thestormdrain main and inflow pipes 184. Depending on the topography of thestormwater collection system for which the apparatus 100 is going to beconnected, the position of the stormwater collection system inflow pipe184 and stormwater collection system outflow pipe 292 may beadvantageously altered and placed in different positions on the junctionbox 470/bypass manhole 400, as apparent to one of ordinary skill in theart, in order to minimize the footprint of the apparatus 100.

As would be apparent to one of ordinary skill in the art, the apparatusshould typically be designed to withstand an AASHTO (“AmericanAssociation of State Highway and Transportation Officials”) or ASTM(“American Society for Testing and Materials”) C 890 H-20 trafficloading with 1.0′-6.0′ of earth cover. The apparatus is flexible and canbe designed to withstand other anticipated loads as designated by thesite engineer and specific site requirements.

To ensure acceptable hydraulic loading rates, promotion of settling andretention of pollutants, and enable proper maintenance, the minimumpermanent pool liquid depth is typically between 1′ to 3′, or larger forlarge embodiments of the apparatus. To provide a minimum hydraulicloading ratio in order to promote the settling of particles from thestormwater flow, there is typically a minimum of approximately onesquare foot of surface area for about each about 60 gallons of totalliquid capacity.

The apparatus typically has a minimum of three access openings formaintenance, preferably at the inlet section, center section, and outletsection, but the number of openings is foreseen to vary based on siterequirements. Openings typically have a minimum clear opening of about30″ in diameter, and are typically located over each compartment of theapparatus. There typically is an additional access opening for everyabout 8′ of interception length in the center section of the apparatus.In one embodiment, there typically is an additional access opening onthe bypass manhole and outlet box.

The disclosed apparatus offers the designer and the developer a newdegree of freedom in solving a large number of stormwater qualityproblem situations. Most existing structural stormwater treatmentsystems rely on a flow through rate calculation to size theirtechnologies, thereby not fully considering the hydraulic or waterquality impacts on the receiving waters. The method, as defined in“Urban Runoff Quality Management,” WEF Manual of Practice No. 23, andASCE Manual and Report on Engineering Practice No. 87, addresses theseconcerns. Those concerns have previously defied reasonable economicalsolutions using previously available structural stormwater mitigationsystems, but are advantageously resolved by the present apparatus.

This method may also be modified, as known to artisans of ordinaryskill, for example, to allow sizing of the capture volume using the meanrunoff volume as defined, for instance, by Discroll, et al. 1989 and toaccommodate an approximate recommended six hour drain down time.

The capture volume stacked water column provides the most efficient useof available system footprint. Owing to this feature, the apparatustypically requires a minimum of about three feet, and preferably aboutfive feet, of vertical temporary water storage capacity, as apparent toartisans of ordinary skill. This temporary stacked water column isaccomplished in the standard apparatus arrangements by use of a bypassweir sized to provide a minimum of backwater while insuring the fullcapture volume potential of the selected vault. Alternate systemconfigurations accomplish the stacked water column configuration byproviding the necessary vertical separation within the stormdrain pipingsystem itself or by using a pumped system. These systems can use, forexample, an external bypass, an internal bypass, a surface bypass,pumped discharge, and/or a bypass with a fall system.

As is typically known to those of skill in the art, the externalapparatus “bypass with weir” configuration is advantageously with thevault aligned parallel to and offset approximately three feet clear fromthe collection stormdrain that is to be intercepted. The bypass manholeis, in one embodiment, located approximately eight feet up gradient fromthe apparatus influent. The size of the bypass manhole and weirelevation relative to the apparatus is typically established by themaximum design flow rate in the collection stormdrain that is to beintercepted.

For example, in one embodiment, as familiar to one of skill in the art,the influent pipe typically has a minimum of about 1% slope to theapparatus, and is preferably constructed of SDR-35 PVC. The influentpipe typically exits the bypass manhole at about 45 degrees to thestormdrain flowline with, in one embodiment, a ⅛-turn elbow located nearthe apparatus. The effluent pipe is typically about 8″ SDR 35 PVC andhas a slope at about 1% from the apparatus to the junction box, sizedequivalent to the bypass manhole. The orifice operating head istypically calculated from the vault soffit to the springline of theeffluent pipe. Due to the fact that the apparatus operates with asurcharge water column, all pipe sizes and angles are based on smoothwall SDR 35 PVC pipe in order to advantageously provide a flexiblewatertight connections a all penetrations. However, other constructionsare also useable based on specific site conditions and requirements, asknown to artisans of ordinary skill in the art.

A junction box is, in one embodiment and as familiar to one of skill inthe art, approximately parallel, approximately 3 feet clear from thecollection stormdrain, and approximately 8 feet down gradient from theapparatus effluent. The size of the junction box is established by thedesign flow rate in the collection stormdrain, maximum pipe sizepenetrations and relative piping angles, and is similar to thosetypically used for the “bypass manhole.”

The “bypass with fall” arrangement is similar to the standardconfiguration with regard to the bypass manhole, junction box andinfluent/effluent pipe sizes. However, the bypass manhole does notrequire a weir in this arrangement. The orifice operating head iscalculated from the vault soffit to the springline of the effluent pipe.

The “pumped discharge” arrangement is also similar to the standardconfiguration with the bypass manhole, by-pass pipe elevation andjunction box, except that the effluent is discharged through a duplexpump system uniquely designed to be contained within the apparatus orjunction box.

The pump positive operating head is calculated from the vault soffit.The pump discharge rate is calculated based on the outflow rate form theapparatus.

The “surface by-pass” is unique in that because by definition theflowline of the storm drainage is on surface above the apparatus. Theorifice operating head is calculated from the surface hydraulic gradeline to the springline of the effluent pipe. While this arrangement doesnot require a dedicated bypass manhole or junction box it does require adrop inlet or catch basin at similar locations to the turning manholesas shown on the “overflow with weir” arrangement.

The preferred “standard internal bypass” configuration, as shown in FIG.10, is with the vault aligned perpendicular to the collection stormdrainthat is to be intercepted. The bypass headworks is so configured toprovide a minimum footprint while allowing for a trash and debriscollection assembly to be incorporated into the apparatus treatmenttrain. The size of the bypass headworks and weir elevation relative tothe apparatus shall be established by the maximum design flow rate inthe collection stormdrain that is to be intercepted. The headworks sizecorresponds to the minimum required for the size, location and materialsof the stormdrain main and influent pipes. The orifice operating head iscalculated from the vault soffit to the springline of the effluent pipe.

The description given herein describes particular embodiments of thepresent apparatus, and other embodiments are foreseen and includedherein and can be adapted by artisans of ordinary skill in the art, suchthat the present invention should be defined only by the followingclaims and equivalents thereof.

What is claimed is:
 1. A stormwater treatment apparatus, comprising: areceptacle adapted to receive water flowing from a surface drainagearea, comprising: the receptacle having a bottom wall and a top wall; aninlet, the inlet supplying water to the receptacle; an outlet, theoutlet passing water out of the receptacle; the inlet and the outletbeing in fluid communication with one another; a permanent pool, thepermanent pool defined by at least the bottom wall of the receptacle,and extending upward from said bottom wall to the height of said outlet,the permanent pool forming a region of reduced flow velocity to trapsediments therein; an inactive pool, the inactive pool defined by atleast the permanent pool, a first baffle extending from the bottom wall,a second baffle extending from the bottom wall, and the bottom wall ofthe receptacle; and an active pool, the active pool defined by at leastthe top wall of the receptacle, and extending downward from said topwall to at least the height of said outlet.
 2. A stormwater treatmentapparatus, comprising: a receptacle adapted to receive water flowingfrom a surface drainage area, comprising: the receptacle having a bottomwall and a top wall; an inlet, the inlet supplying water to thereceptacle; an outlet, the outlet passing water out of the receptacle;the inlet and the outlet being in fluid communication with one another;a permanent pool, the permanent pool defined by at least the bottom wallof the receptacle, and extending upward from said bottom wall to theheight of said outlet, the permanent pool forming a region of reducedflow velocity to trap sediments therein; an inactive pool, the inactivepool defined by at least the permanent pool, a first baffle extendingfrom the bottom wall, a second baffle extending from the bottom wall,and the bottom wall of the receptacle; and an overflow structure, theoverflow structure diverting excess stormwater from the receptacle,wherein the overflow structure includes a control weir and an apparatusinlet, and the overflow structure is integral with the receptacle. 3.The apparatus of claim 2, wherein the integral overflow structureincludes a stormwater collection inflow pipe and a stormwater collectionoutflow pipe.
 4. The apparatus of claim 2, wherein the integral overflowstructure includes an apparatus outlet pipe, the apparatus outlet pipereturning water treated in the receptacle to the overflow structure. 5.The apparatus of claim 2, further comprising a bypass pipe, the controlweir regulating the diversion of water to the bypass pipe.
 6. Astormwater treatment apparatus, comprising: a receptacle adapted toreceive water flowing from a surface drainage area, the receptaclehaving at least a top and a bottom; an inlet section, the inlet sectionsupplying water to the receptacle; an outlet section, the outlet sectionpassing water out of the receptacle; at least one mid section, the atleast one mid section comprising a fluid communication between the inletsection and the outlet section; a permanent pool, the permanent pooldefined by at least the bottom wall of the receptacle, and extendingupward from said bottom wall to at least the height of said outlet; thepermanent pool generally below the path of fluid communication; thepermanent pool forming a region of reduced flow velocity to trapsediments therein; an inactive pool, the inactive pool defined by atleast the permanent pool, a first baffle extending from the bottom ofthe receptacle, a second baffle extending from the bottom of thereceptacle, and the bottom of the receptacle, wherein at least a firstportion of the first baffle is at an angle of between about thirtydegrees and about sixty degrees with the bottom of the receptacle and atleast a second portion of the first baffle is at an angle of roughlyninety degrees with the bottom of the receptacle.
 7. A stormwatertreatment apparatus, comprising: a receptacle adapted to receive waterflowing from a surface drainage area, the receptacle having at least atop and a bottom; an inlet section, the inlet section supplying water tothe receptacle; an outlet section, the outlet section passing water outof the receptacle; at least one mid section, the at least one midsection comprising a fluid communication between the inlet section andthe outlet section; a permanent pool, the permanent pool defined by atleast the bottom wall of the receptacle, and extending upward from saidbottom wall to at least the height of said outlet; the permanent poolgenerally below the path of fluid communication; the permanent poolforming a region of reduced flow velocity to trap sediments therein; andan inactive pool, the inactive pool defined by at least the permanentpool, a first baffle extending from the bottom of the receptacle, asecond baffle extending from the bottom of the receptacle, and thebottom of the receptacle, wherein at least a first portion of the secondbaffle is at an angle of between thirty degrees and sixty degrees withthe bottom of the receptacle, and at least a second portion of thesecond baffle is at an angle of roughly ninety degrees with the bottomof the receptacle.
 8. A stormwater treatment apparatus, comprising: areceptacle adapted to receive water flowing from a surface drainagearea, the receptacle having at least a top and a bottom; an inletsection, the inlet section supplying water to the receptacle; an outletsection, the outlet section passing water out of the receptacle; atleast one mid section, the at least one mid section comprising a fluidcommunication between the inlet section and the outlet section; apermanent pool, the permanent pool defined by at least the bottom wallof the receptacle, and extending upward from said bottom wall to atleast the height of said outlet; the permanent pool generally below thepath of fluid communication; the permanent pool forming a region ofreduced flow velocity to trap sediments therein; an inactive pool, theinactive pool defined by at least the permanent pool, a first baffleextending from the bottom of the receptacle, a second baffle extendingfrom the bottom of the receptacle, and the bottom of the receptacle; athird baffle, the third baffle near said inlet, the third baffleextending down from the top wall of the receptacle; and, a fourthbaffle, the fourth baffle near said outlet, the fourth baffle extendingdown from the top wall of the receptacle.
 9. A stormwater treatmentapparatus, comprising: a receptacle adapted to receive water flowingfrom a surface drainage area; the receptacle having a bottom, a top, anda perimeter; the receptacle having an inlet and an outlet; the inlet andthe outlet being in fluid communication with one another; an activepool, the active pool defined by at least the top wall of thereceptacle, the perimeter of the receptacle, and extending downward fromsaid top wall to at least the height of said outlet, the active pool aregion of fluid communication between the inlet and the outlet; apermanent pool, the permanent pool a region of little or no flowgravitationally beneath the active pool to trap sediments therein; andthe outlet includes an overflow structure, said overflow structurediverting excess stormwater from said receptacle when said receptacle isat or near full the overflow structure not substantially affecting theperformance of the active pool, the overflow structure includes anapparatus outlet pipe, the apparatus outlet pipe returning water treatedin the receptacle to the overflow structure.
 10. A stormwater treatmentapparatus, comprising: a receptacle adapted to receive water flowingfrom a surface drainage area; the receptacle having a bottom, a top, anda perimeter; the receptacle having an inlet and an outlet, the outletincluding an oriface smaller than the inlet, the receptacle having aninlet, the inlet including an integral overflow structure, said overflowstructure diverting excess stormwater from said receptacle when saidreceptacle is at or near full; the inlet and the outlet being in fluidcommunication with one another; an active pool, the active pool is aregion defined by the top of the receptacle, the sides of thereceptacle, and at least the height of the outlet; a permanent pool, thepermanent pool a region of little or no flow beneath the active pool totrap at least small sediments therein; and, an inactive pool, theinactive pool a region defined by the permanent pool, at least a firstbaffle attached to the bottom of the receptacle, a second baffleattached to the bottom of the receptacle, the sides of the receptacle,and the bottom of the receptacle.
 11. The apparatus of claim 10, whereinat least a first portion of the second baffle is at an angle of betweenthirty degrees and sixty degrees with the bottom of the receptacle. 12.The apparatus of claim 10, wherein at least a first portion of the firstbaffle is at an angle of about forty-five degrees with the bottom of thereceptacle.
 13. The apparatus of claim 10, wherein at least a firstportion of the second baffle is at an angle of about forty-five degreeswith the bottom of the receptacle.
 14. The apparatus of claim 12,wherein at least a second portion of the first baffle is at an angle ofroughly ninety degrees with the bottom of the receptacle.
 15. Theapparatus of claim 13, wherein at least a second portion of the secondbaffle is at an angle of roughly ninety degrees with the bottom of thereceptacle.
 16. The apparatus of claim 10, wherein the apparatus has avolume of at least 500 cubic feet.
 17. An apparatus for separation ofpollutants in runoff that are less and more dense than the runoff water,comprising: a receptacle adapted to receive stormwater runoff flowingfrom surface areas tributary to it, the receptacle having a bottom and atop, a left side-wall and a right side-wall, and a front side-wall andend side-wall, forming a rectangular tank; an inlet for introducingstormwater flowing from tributary surface areas into the receptacle andan outlet for discharging water; at least four baffles positioned withinthe receptacle between the inlet and the outlet, with all of the bafflesattached to both sides of the receptacle, with at least two bafflesattached to the bottom of the receptacle and not attached to the top, atleast one baffle attached to the top of the receptacle and not attachedto the bottom, and at least one baffle that is not attached to thebottom and top of the receptacle; an inlet section for receiving water,for decreasing energy of the flowing water, and for uniformlydistributing water across the width of the receptacle; one or moremidsections for trapping materials more dense than water that settle outof water by gravity and for trapping materials less dense than waterthat rise to the surface of water by gravitational separation; an outletsection for discharging water at a controlled rate and for excludingmaterials more and less dense than water being discharged, the outletsection including an opening located on the end side-wall that allowswater in the apparatus to discharge, the outlet substantially smallerthan the inlet; a mesh screening, the mesh screening from the bottom tothe top of the apparatus is attached in a removable fashion to the endside-wall to form a barrier through which any water that dischargesthrough the opening must pass prior to discharge; an overflow structure,the overflow structure diverting excess stormwater flow from thereceptacle, the overflow structure integral with the receptacle; anactive pool, the active pool defined by at least the top wall of thereceptacle, and extending downward from said top wall to at least theheight of said outlet opening; a permanent pool, the permanent pooldefined by at least the bottom wall of the receptacle, and extendingupward to at least the height of said outlet opening; and, an inactivepool, the inactive pool defined by at least the permanent pool, thebottom of the receptacle, and the at least two baffles attached to thebottom of the receptacle.
 18. A stormwater treatment apparatus,comprising: a receptacle having a top, a bottom, a left side wall and aright side wall, an inlet side wall and an outlet end wall, saidreceptacle comprising an inlet section, an outlet section and at leastone midsection between said inlet section and said outlet section; aninlet located in said inlet section, spaced above said bottom; an outletlocated in said outlet section spaced above said bottom, said outletheight defining a permanent pool water surface elevation level; a firstbaffle having an upstream side and a downstream side, said first baffleconnected to said bottom and extending upward no higher than saidpermanent pool water surface elevation level, said upstream side of saidfirst baffle including at least a portion angled upward from said bottomand towards said outlet; a second baffle between said first baffle andsaid outlet having an upstream side and a downstream side, said secondbaffle connected to said bottom and extending upward no higher than saidpermanent pool water surface elevation level, said upstream side of saidsecond baffle including at least a portion angled upward from saidbottom and toward said outlet; an active pool, said active pool definedby said inlet, said outlet, and said top of said receptacle; and, apermanent pool, said permanent pool defined by said first baffle, saidsecond baffle, said left side wall, said right side wall, and saidpermanent pool water surface elevation level, said permanent poolgenerally gravitationally below said active pool.